The invention relates to an apparatus for detecting a position and a format of a film cassette inserted into the apparatus, and in particular, to a drawer apparatus for an x-ray system adapted to receive an x-ray film cassette.
Drawer apparatuses, in particular, catapult frame drawers for x-ray film cassettes, are known. Catapult frame drawers are typically mounted in x-ray receptacle spaces in a manner similar to drawers. By pulling them out, a human operator or user can substantially quickly load film cassettes or take exposed film cassettes out. Simple, fast handling, which is often indispensable in the field of medical diagnosis, is made possible by such drawer-like systems.
Film cassettes exist in various formats and sizes, which are used depending on a targeted application. For instance, to take an x-ray of an extremity of a patient, a smaller film cassette may suffice, while for a chest film, a larger-area film cassette may be necessary. To make them adaptably flexible for many possible applications, catapult frame drawers are designed to be large enough to be suitable for many different cassette formats.
Taking an x-ray may require substantial, exact positioning of the film cassette in the catapult frame drawer. As such, mechanical guides may be provided to place or situate an inserted film cassette in a desired position. The film cassette positioning may be readily possible if film cassettes of the same format and size are used throughout. However difficulties in handling may arise when varying formats and sizes are used. First, the mechanical guides may need to be designed so flexibly that they can easily be adapted to various cassettes. The cassette adaptation may require additional handling steps in fitting the film cassette into the guides, which may make it complicated to change film cassettes quickly. Second, the format and size of an inserted film cassette cannot be seen by the operator from outside when the frame drawer is closed, and automatic detection is therefore desirable.
An x-ray apparatus with a holder for x-ray film cassettes that enables automatic detection of the cassette dimensions is known from German Patent Disclosure DE 34 28 747 A1. For detecting a length and width of the film cassette, two pivotable levers are provided, which are pressed by spring force against two side faces of the film cassette. Further, a respective position of the two pivotable levers at a given time may be dependent on dimensions of the inserted cassette and may be detected via adjustable electrical resistors or capacitors. The automatic detection of the film cassette in the x-ray apparatus employs electromechanical means or units that are complicated to produce and are subject to wear.
To minimize these problems, it is known from German Patent Disclosure DE 43 32 428 A1 to detect the format of the film cassette by using photoelectric barriers. As such, a photoelectric barrier array in which a plurality of photoelectric barriers is arranged in two dimensions is provided. The accuracy of the format detection depends on the number of photoelectric barriers used. If a wide range of variation of formats is to be differentially detected, a large number of photoelectric barriers are thus necessary.
Accordingly, the known apparatuses for detecting the format of film cassettes are complicated to produce. Moreover, these apparatuses offer no flexibility for future adaptation to film cassette formats that may change in the future. Moreover, these apparatuses make it possible to detect only the format, but not the position, of an inserted film cassette.